1. Field of the Invention
The present invention generally relates to a refrigerant compressor and, more particularly, to a slant plate type compressor, such as a wobble plate type compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system.
2. Description of the Prior Art
A slant plate type refrigerant compressor with a variable displacement mechanism suitable for use in an automotive air conditioning system is disclosed in Japanese Patent Application Publication No. 1-142277. As disclosed therein, the compression ratio of the compressor may be controlled by changing the slant angle of the sloping surface of the wobble plate. The slant angle of the wobble plate is adjusted so as to maintain a constant suction pressure in response to changes in the pressure differential between the suction chamber and the crank chamber.
Referring to FIG. 1, compressor 10 includes cylindrical housing assembly 20 including cylinder block 21, front end plate 23 disposed at one end of cylinder block 21, crank chamber 22 formed between cylinder block 21 and front end plate 23, and rear end plate 24 attached to the other end of cylinder block 21. Front end plate 23 is secured to one end of cylinder block 21 by a plurality of bolts 101. Rear end plate 24 is secured to the opposite end of cylinder block 21 by a plurality of bolts 102. Valve plate 25 is disposed between rear end plate 24 and cylinder block 21. Opening 231 is centrally formed in front end plate 23 for rotatably supporting drive shaft 26 through bearing 30 disposed therein. The inner end portion of drive shaft 26 is rotatably supported by bearing 31 disposed within central bore 210 of cylinder block 21. Bore 210 extends to a rearward (to the right in FIG. 1) end surface of cylinder block 21 and houses valve control mechanism 19.
Cam rotor 40 is fixed on drive shaft 26 by pin member 261 and rotates therewith. Thrust needle bearing 32 is disposed between the inner end surface of front end plate 23 and the adjacent axial end surface of cam rotor 40. Slant plate 50 is disposed adjacent cam rotor 40 and includes opening 53 through which drive shaft 26 passes.
Referring to FIGS. 2 and 3, a hinged joint mechanism coupling cam rotor 40 and slant plate 50 is shown. Slant plate 50 includes arm 51 having first and second axial end surfaces 51a and 51b. Cam rotor 40 includes arm 41 which includes first and second cylindrical projections 411 and 412 axially projecting from the opposite end surfaces of a terminal end portion of arm 41. Hole 413 is axially bored through the terminal end portion of arm 41. Pin member 42 includes shaft portion 42a and head portion 42b having a diameter greater than the diameter of shaft portion 42a. Shaft portion 42a of pin member 42 loosely penetrates through slot 52 of arm 51. Hole 413 of arm 41 of cam rotor 40 fixedly receives shaft portion 42a of pin member 42 by forcible insertion. Snap ring 43 is fixedly secured to one end region of shaft portion 42a opposite to head portion 42b. Arm 41 of cam rotor 40, pin member 42 and slot 52 of arm 51 of slant plate 50 form a hinged joint mechanism. Pin member 42 slides within the slot 52 to allow adjustment of the angular position of slant plate 50 with respect to the longitudinal axis of drive shaft 26. Axial movement of arm 51 of slant plate 50 is limited by head portion 42b of pin member 42 and cylindrical projection 412 of arm 41 of rotor 40. Arm 41 of rotor 40 is made of cast iron. Pin member 42 and arm 51 of slant plate 50 are made of steel.
Wobble plate 60 is rotatably mounted on slant plate 50 through bearings 61 and 62. Fork shaped slider 63 is attached to the outer peripheral end of wobble plate 60 by pin member 64 and is slidably mounted on sliding rail 65 disposed between front end plate 23 and cylinder block 21. Fork shaped slider 63 prevents rotation of wobble plate 60. Wobble plate 60 nutates along rail 65 when cam rotor 40 rotates. Cylinder block 21 includes a plurality of peripherally located cylinder chambers 70 in which pistons 71 reciprocate. Each piston 71 is coupled to wobble plate 60 by a corresponding connection rod 72.
A pair of seamless piston rings 73 made of polytetrafluoroethylene is disposed at an outer peripheral surface of piston 71. Piston rings 73 prevent the wear of both aluminum alloy piston 71 and aluminum alloy cylinder block 21 due to friction therebetween and prevent any direct contact between pistons 71 and the inner surface of cylinder 70.
Rear end plate 24 includes peripherally positioned annular suction chamber 241 and centrally positioned discharge chamber 251. Valve plate 25 is located between cylinder block 21 and rear end plate 24 and includes a plurality of valved suction ports 242 linking suction chamber 241 with respective cylinders 70. Valve plate 25 also includes a plurality of valved discharge ports 252 linking discharge chamber 251 with respective cylinders 70. Suction ports 242 and discharge ports 252 are provided with suitable reed valves as described in U.S. Pat. No. 4,011,029 to Shimizu.
Suction chamber 241 includes inlet portion 241a which is connected to an evaporator (not shown) of an external cooling circuit (not shown). Discharge chamber 251 is provided with outlet portion 251a connected to a condenser (not shown) of the cooling circuit (not shown). Gaskets 27 and 28 are positioned between cylinder block 21 and the inner surface of valve plate 25 and the outer surface of valve plate 25 and rear end plate 24, respectively. Gaskets 27 and 28 seal the mating surfaces of cylinder block 21, valve plate 25 and rear end plate 24. Gaskets 27 and 28 and valve plate 25 form a valve plate assembly 200.
A first communication path linking crank chamber 22 and suction chamber 241 is formed in cylinder block 21. This first communication path includes valve control mechanism 19 which includes cup-shaped casing 191 which defines valve chamber 192 therein. O-ring 19a is disposed between an outer surface of casing 191 and an inner surface of bore 210 to seal the mating surface of casing 191 and cylinder block 21. A plurality of holes 19b are formed at the closed end (to the left in FIG. 1) of cup-shaped casing 191 to permit crank chamber pressure into valve chamber 192 through gap 31a existing between bearing 31 and cylinder block 21. Circular plate 194 having hole 194a formed at the center thereof is fixed to the open end of cup-shaped casing 191. Bellows 193, which is disposed within valve chamber 192, contracts and expands longitudinally in response to the crank chamber pressure. The forward (to the left in FIG. 1) end of bellows 193 is fixed to the closed end of casing member 191. VaLve member 193a is attached at rearward (to the right in FIG. 1) end of bellows 193 to selectively control the opening and closing of hole 194a. Valve chamber 192 and suction chamber 241 are linked by hole 194a, central portion 211 of bore 210, conduit 195 formed in cylinder block 21 and hole 196 formed in valve plate assembly 200. Valve retainer 15 is secured to the rear end surface of valve plate assembly 200 by bolts 151.
Communication path 18, which is bored longitudinally from a forward end surface of cylinder block 21 to a rear end surface of valve retainer 15, is a second communication path formed in the cylinder block to link discharge chamber 251 to crank chamber 22. Communication path 18 controls the flow of refrigerant gas from discharge chamber 251 to crank chamber 22. Large diameter conduit portion 181 of communication path 18 has filter screen 182 disposed therein. Capillary tube 183, which performs a throttling function to reduce the pressure of refrigerant gas from discharge chamber 251 to crank chamber 22, is fixed within communication path 18 and is coupled to filter screen 182.
During operation of compressor 10, drive shaft 26 is rotated by the engine of the vehicle (not shown) through electromagnetic clutch 300. Cam rotor 40 is rotated with drive shaft 26 causing slant plate 50 to rotate. The rotation of slant plate 50 causes wobble plate 60 to nutate. The nutating motion of wobble plate 60 reciprocates pistons 71 in their respective cylinders 70. As pistons 71 are reciprocated, refrigerant gas which is introduced into suction chamber 241 through inlet portion 241a is drawn into cylinders 70 through suction ports 242 and subsequently compressed. The compressed refrigerant gas is discharged from cylinders 70 to discharge chamber 251 through respective discharge ports 252 and then into the cooling circuit through outlet portion 251a. A portion of the discharged refrigerant gas in discharge chamber 251 continuously flows into crank chamber 22 through conduit 18 at a reduced pressure as a function of capillary tube 183.
Valve control mechanism 19 is responsive to the pressure in crank chamber 22. When the pressure in crank chamber 22 exceeds a predetermined value, hole 194a is opened by the contraction of bellows 193. The opening of hole 194a permits fluid communication between crank chamber 22 and suction chamber 241. As a result, the slant angle of slant plate 50 increases to maximize the displacement of the compressor. However, when the pressure in crank chamber 22 is less than a predetermined value, hole 194a is closed by valve member 193a of bellows 193. This action blocks communication between crank chamber 22 and suction chamber 241. As a result, the slant angle of slant plate 50 is controlled by changes in the pressure in crank chamber 22 to vary the displacement of the compressor.
With respect to the hinged joint mechanism, an outer peripheral surface of shaft portion 42a of pin member 42 and an inner wall of slot 52 of arm 51 frictionally slide against each other. Furthermore, first axial end surface 51a of arm 51 and the axial end surface of second cylindrical projection 412 of arm 41 frictionally slide against each other, and second axial end surface 51b of arm 51 and an inner end surface of head portion 42b of pin member 42 also frictionally slide against each other.
Since pin member 42 and arm 51 of slant plate 50 are made of steel, the frictional engagement between the outer peripheral surface of shaft portion 42a of pin member 42 and the inner wall of slot 52 of arm 51 occurs between two hard metals. Similarly, the frictional engagement between the second axial end surface 51b of arm 51 and the inner end surface of head portion 42b of pin member 42 occurs between two hard metals. Therefore, the frictional engagement between pin member 42 and arm 51 of slant plate 50 occurs without causing abnormal abrasion on the frictional contact surfaces of each of pin member 42 and arm 51.
On the other hand, the frictional engagement between first axial end surface 51a of arm 51 and the axial end surface of second cylindrical projection 412 of arm 41 occurs between hard and soft metals. During operation of the compressor, the axial end surface of second cylindrical projection 412 is not uniformly worn away because that area A (as shown in FIG. 4) of the axial end surface of second cylindrical projection 412 more frequently frictionally slides on the axial end surface of second cylindrical projection 412. Therefore, durability of the hinged joint mechanism between rotor 40 and slant plate 50 abnormally decreases.